LightSail-1™
Solar Sail Design and Qualification
Chris Biddy,
Stellar Exploration Inc.
41st Aerospace Mechanism Symposium
LightSail-1™ Introduction
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Project of The Planetary Society
Completely privately funded through member donations
Objectives are to:
• Demonstrate viability of Solar Sails
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Ability to alter orbit energy in positive direction
Ability to manage orbital energy
Ability to control spacecraft under solar sail power
Develop and demonstrate key technologies
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Sail deployment
Sail material management during flight
Gossamer structure dynamics
• Demonstrate pathway to deep space with solar sails
Requirements are to:
• Achieve greater sail area/mass than COSMOS-1
ACS Orbit Raising Mode
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Orbit raising will be accomplished by 90 degree pitch
maneuver
>800 km orbit needed for SRP > Aerodynamic Drag
LightSail-1™ Design Challenges
• How to package the sail and booms in the
allowable volume
• How to manage boom strain energy while
stowed and during deployment
• How to control the sail deployment
• How to constrain sail material and booms prior
to deployment (including during launch)
• How to manage sail material during deployment
LightSail-1™ Configuration
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3U CubeSat Spacecraft organized into 3
sections
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Avionics Section/Sail Storage (~2U)
– Contains Avionics Board, radio, Sensor
Interface board, Battery Pack, 3- single
axis MEMS Gyros, 3 Torque Rods, 1
Momentum Bias Wheel, a 3 axis
accelerometer, and sail storage cavity
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Deployer Section (~0.5U)
– Houses 4 x 4 meter TRAC booms
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Payload Section (~0.5U)
– Houses boom drive motor and gear train,
storage area for cameras (attached to
deployable arrays), monopole antenna,
deployable array burn wire mechanism
and a 3-axis accelerometer
Boom
• Lightsail-1™ uses the AFRL developed TRAC (Triangular Rollable
and Collapsible) boom
• The TRAC boom can be collapsed and rolled around a spindle
providing a compact storage solution
• Booms “self-deploy” due to stored strain energy however an external
torque is required to deploy the sail
– Booms are driven by a brushless dc motor coupled with worm drive
gear train
Deployed TRAC boom
Boom Deployer
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Key Requirements Store and deploy 4m booms
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Deployer Functions
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Provide normal reaction force against booms at all times (required to keep booms “pinched”)
Provide for smooth deployment (no interference between booms and deployer components)
Guide booms at deployer exit
Deployer Features
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Control deployment rate so as to not damage booms or sail blades
Bearing supported spindle
Rocker arm tensioner with flexure springs
keep booms against spindle
Delrin AF boom guides at deployer exit
Deployer Size
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Maximum height = 5.5 cm
Maximum width = 10 cm
Deployer
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Rocker arms deflect flexure springs during boom winding
Flexures stick out past solar panel plane only at the end of boom
deployment (after solar cell panels are deployed)
Booms exit at corners (denoted by arrows)
Fully deployed state (flexure springs not deflected)
Fully stowed state (flexure springs deflected)
Deployer Lessons Learned
• Significant boom axial force required to deploy sails
• Boom management within deployer critical for reliable
deployment of the sail
– Determined that the flexure spring rate affected required motor
torque to deploy the sail
– Determined that high coefficient of friction is
required between adjacent boom wraps
• Difficult to predict cold performance
– Deployment motor required additional
current as temperature decreased
Flight Deployer and payload section
Sail Folding and Storage
• Sail quadrants are z-folded in two directions to form a wedge shaped folded
cross-section
• Z-fold provides a path for gases to escape
• Verified with vacuum chamber test
Z-fold sail from
center outward
to form
“wedge”
shaped fold
Z-fold sail quadrant from outside edge to
center
Folded sail
quadrants fit
into wedge
shaped
cavities and
restrained by
deployable
Solar Cell
panels
Sail Attachment
• The triangle shaped sail quadrants are attached to the spacecraft at
all three corners
– At the base of the sail storage cavity and the tips of the booms
• Metal grommets and split rings were used to connect the sails to the
booms with extension springs in series to account for thermal
distortions
Sail base grommet
Sail quadrant to boom attachment
Sail Management
• The stowed sail is held in place with the deployable arrays
• During deployment the sail is withdrawn from the storage cavities 1
fold at a time due to a slight interference fit between the folded sail
quadrants and the storage cavity
Remaining Sail Material
Tensioned Sail
TRAC Boom
Stowed Flight unit
Engineering model deployment testing
Qualification Testing
• Qualification testing included sail deployments before and after
TVAC and random vibe tests
• Off-loading was achieved by building a table to support the booms
during testing
LightSail-1 undergoing random
vibration testing at Cal Poly
Sail deployment table
Onboard camera view of sail deployment
Conclusion
• LightSail-1™ is ready for launch
• Reliable sail deployment has been demonstrated (over a dozen
successful deployments)
• LightSail-1™ achieved ~150g/m^2 with an 80:1 pre to post
deployment ratio
Questions?